Insulin is a peptide hormone (molecular weight: approximately 5800) that is produced via a precursor, proinsulin, in the beta cells in the pancreatic islets of Langerhans. Insulin is involved in sugar, amino acid, and fat metabolism, and it is physiologically important in the hypoglycemic effect. Diabetes is caused by insufficient insulin secretion due to decrease in or the functional deterioration of beta cells or due to insufficient insulin action in peripheral tissues. Therefore, the measurement of blood insulin concentration reflecting the insulin secretory function of beta cells is a useful index for the diagnosis and understanding of the clinical condition of diabetes and determination of the cause of abnormal glucose tolerance.
The following techniques are known insulin assays using monoclonal antibodies.
Patent Document 1 discloses a method of quantitating insulin in accordance with an enzyme-linked immunosorbent assay (ELISA). This assay uses a monoclonal antibody bound to an insoluble carrier and a monoclonal antibody not competing with the said antibody for an epitope that is labeled with an enzyme.
Patent Document 2 discloses a method of quantitating insulin in accordance with a particle agglutination immunoassay. This assay uses two monoclonal antibodies that have different recognition sites and are bound to insoluble carriers.
Although both documents disclose methods of assaying insulin using a plurality of monoclonal antibodies that have different recognition sites for insulin, no disclosure is made regarding the cross-reactivity with proinsulin or insulin analogs, such as insulin analog formulations. Therefore, it is not known whether insulin can be measured specifically and sensitively.